TEGUCIGALPA, HONDURAS — People in Honduras‘ predominantly Indian Mosquito Coast region burned down government offices and demanded that U.S. drug agents leave the area.

They were reacting angrily to an anti-drug operation in which they say police gunfire killed four innocent people, including two pregnant women.

The anger is aimed at Honduran authorities and the U.S. Drug Enforcement Administration (DEA), which confirmed Wednesday that some of its agents were in a U.S.-owned helicopter with Honduran police officers when the shooting happened last Friday on the Patuca River in northeastern Honduras.

Honduran and U.S. officials said only the police officers on the anti-drug mission fired their weapons, and not until the helicopter was shot at first. The officials said the aircraft was chasing a small boat suspected of carrying drugs on the river.

Local officials said the two men and two pregnant women killed weren’t drug smugglers. They said the victims were diving for lobster and shellfish.

“These innocent residents were not involved in the drug problem, were in their boat going about their daily fishing activities … when they gunned them down from the air,” Lucio Vaquedano, mayor of the coastal town of Ahuas, said in a telephone interview Wednesday.

Recounting the burning of government offices in the northern Gracias a Dios region, Mr. Vaquedano said: “Some of the inhabitants reacted with anger at the attack, and sought revenge against the government.”

The leaders of the Masta, Diunat, Rayaka, Batiasta and Bamiasta ethnic groups said in a press statement that “the people in that canoe were fishermen, not drug traffickers.”

“For centuries we have been a peaceful people who live in harmony with nature, but today we declared these Americans to be persona non grata in our territory,” the statement continued.

Ricardo Ramirez, chief of Honduras‘ national police force, said the operation “was carried out with the support of the DEA,” and alleged the occupants of the boat were transporting drugs and fired at the helicopter.

Chief Ramirez said an assault rifle was seized at the scene.

DEA officials acknowledged their agents were working with Honduran police aboard the helicopter. “We were there in a support role, working with our counterparts,” DEA spokeswoman Dawn Dearden said in Washington.

U.S. government officials, speaking on the condition of anonymity because their statements had not been authorized, said Honduran law enforcement did not initiate the shooting, but rather returned fire after being attacked. The officials said the DEA agents did not fire.